// Press Shift twice to open the Search Everywhere dialog and type `show whitespaces`,
// then press Enter. You can now see whitespace characters in your code.
public class Main {
    public static void main(String[] args) {
        MobileTelephone m = new MobileTelephone();
        SIM s1 = new SIMOfChinaMoblie();
        m.useSIM(s1);
        m.print();

        SIM s2 = new SIMOfChinaUnicom();
        m.useSIM(s2);
        m.print();
    }
}